Tone control system



Sept. 28,' 1937. v. D. LANDON TONE CONTROL SYSTEM Filed Feb. 28, 1935aow cum. cem. @wm acm e2 o3 om. o H n Y M 0 @Nl n .MN .quoo H N 1M M..ow.. n. m .-m w a M d. Qomwm. T .m a.. 1 d D bl I n W n HESSEN w m 0 n.me arb a1 owm \.\1 i. V n u @nimm 3 B um. l um Hm. www mm. hm.

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b QN Patented Sept. 28, 193i UNITED STATES PATENT OFFICE TONE CONTROLSYSTEM tion of Delaware Application February 28, 1935, Serial No. 8,711

10 Claims.

The present invention relates to tone control systems for radioreceiving apparatus and the like, and has for its primary object toprovide an improved automatic tone control system for 5 apparatus of thecharacter above referred to, for` v-arying the audio frequency responserange thereof with variations in signal strength and/ or variations inpercentage modulation, without introducing harmonic distortion.

It is a further object of the present invention, to provide a tonecontrol system for radio receiving apparatus and the like which operatesautomatically in response to variations in signal strength and/orpercentage modulation to control the audio frequency responsecharacteristic thereof in a manner to decrease the reproduction ofelectrical and other disturbances causing noise. More specifically, asystem of this character may operate automatically to reduce the audiofrequency output in the higher audio frequency range in response to weaksignals or low percentage modulation.

It is a still further object of the present invention, to provide animproved tone control system which is responsive to both modulation andcarrier wave variations in a received modulated high frequency signal.

It is also an object of the present invention, to provide an improvedtone control system for radio receiving apparatus and the like providinga variable audio frequency band width which is a function of percentagemodulation as well as carrier wave length.

It is also an object of the invention, to provide an improved tonecontrol network, including an electric discharge amplifier device as acontrol element therein, and means for deriving rectified controllingpotentials therefor from high frequency and low or audio frequencysignals, together with means for varying the degree of control from eachof said sources. The invention, will, however, be better understood fromthe following description when considered in connection r with theaccompanying drawing and its scope will be pointed out in the appendedclaims. In

the drawing Figure 1 is a schematic circuit diagram of a portion of aradio receiving system embodying the invention, and

50 Fig. 2 is a curve diagram illustrating further operatingcharacteristics thereof.

Referring to Fig. 1, 5 is a high frequency rectiiier or detector formodulated high frequency signals, and is preferably of the dioderectifier 55 type having a 4cathode 'I and a rectifier anode (Cl.Z50-20) 9. The rectifier is supplied with modulated high frequencysignals through a tuned input circuit I0, the high side of which isconnected with the anode and the low side of which is connected with thecathode through a rectifier output im- 5 pedance or resistor II. Oneterminal I3, of the resistor is connected to the cathode and theopposite terminal I5, is connected with the input circuit Ill throughsuitable high frequency filter means comprising a series resistor I1 andbypass condensers I3 to cathode.

Modulated high frequency signals are applied to the input circuit I0through a coupling device such as a tuned transformer 2i, having inputterminals 23. In the present example, this may be the intermediatefrequency amplifier output transformer and the device 5 may representthe second detector of a superheterodyne receiver.

The high frequency rectifier device or detector 5 is also provided witha triode lcontrol grid 25 and output anode 2'I associated with thecathode I for amplifying the rectified signal or modulation componentand, for this purpose, the grid 25 is directly connected through a lead29 with the rectifier output impedance II from which it also receives abiasing potential in response to signals. The connection for the lead 29with the impedance I I is adjustable through a contact 3I, whereby the-amount of biasing potential and the amplitude of the modulation oraudio frequency signals to be amplified may be varied.

A modulation or audio frequency transmission circuit for connecting thedetector device 5 with a succeeding utilization device such as a secondstage amplifier device 33 is indicated at 35. This circuit is connectedwith the output anode 2l of the amplifier portion of the device 5, andincludes an anode coupling resistor 31 through which anode potential issupplied to the anode 2l, a coupling condenser 3S for the anode resistor3l, a volume control potentiometer resistor 4I having grounded returnconnections 43 and 45 with the cathode T through a return lead 4'I forthe cathode. The grid of the amplifier device 33 is connected to avariable tap 49 on the volume control resistor 4I and the cathodethereof is grounded as indicated at 5I. The volume control potentiometer4l is preferably provided with a tone compensatingnetwork indicated at53 for 50 the purpose of reducing the amplitude of signals in theintermediate portions of the audio frequency range simultaneously with areduction in the volume control adjustment. The audio frequency outputcircuit for the device 33 is indi- 55 cated at 55 and 51 and is providedwith output terminals 59.

A tone control network is connected across the audio frequencytransmission circuit betweeny the lead and ground and, in the presentexample, includes a high frequency tone control condenser 6| connectedon one side with the lead 35 and on the opposite side with the anode 63of a pentode type electric discharge ampliiier device 55, the cathode ofwhich is connected to ground through the lead 41. The device 65 isprovided with a control grid 69, a screen grid il and a suppressor grid13. rI'he anode 63 is connected with an anode circuit impedance orresistor 15 which is provided with an anode return circuit connectionthrough an anode potential supply lead 11, a tap connection 19 on apotential supply source such as a resistor 8|, a grounded tap connection83 thereon, the ground connection 45 and the cathode return lead 41. Animpedance device or choke coil 85 is preferably connected in shunt withthe resistor 15 in the anode circuit, as indicated, as an impedancelimiting means.

The potential supply resistor 8| is supplied with direct current throughterminals 81 having a f'. polarity as indicated. It will be noted thatthe ground connection 83 is located at a tap point 89 between theterminals 81 to provide a negative bias potential supply section betweenthe negative terminal and the tap point 89. The anode lead 1;'11receives an operating potential from a tap point 9|, and the anodecircuit 51 for the device 33 is also connected to the positive terminal,the anode potentials being provided between the tap point 89 and thepositive terminal. The

voltage divider resistor 8| represents any suitable grounded source forsupplying positive operating potentials and negative biasing potentialsfor an electric discharge amplifier system.

From the foregoing description it will be seen @that the tone controlnetwork for the audio frequency transmission circuit 35 is controlled bythe plate impedance of the electric discharge amplier device 65. In thepresent network, variation of the anode impedance of the device 65 1causes the condenser 6| to become more or less effective as a shunt tonecontrol means for reducing the amplitude of signals in the highfrequency end of the audio frequency range as the anode impedance of thedevice 65 is decreased.

In accordance with the invention, the device 65 is of the pentode typeand further, is preferably ofthe multi-mu or gradual cut-olf type. Forexample, it may preferably be provided by a tube known commercially asan RCA-58 tube. For a condition of no signal and maximum sensitivity,the anode impedance of the device 65 is initially adjusted to arelatively low value. In the present example this serves to reduce thehigh frequency response to a point where the noise transmission issufficiently low to render it unobjectionable. The anode impedance islowered by placing a. negative biasing potential on the suppressor grid13 y through a connection lead 93 having a variable tap connection withthe neg- `ative bias supply section of the source 8|. For

flthrough a supply lead 91 and tap 99 of substantially volts positivewith respect tothe cathode.

The. plate impedance of the device 65, ordi- 75Mnarily relatively high,is adjusted by the above titl 4 under such conditions of operation.

In order that the audio frequency response characteristic of the systemmay be varied automatically in response to changes in the amplitude of areceived carrier wave, that is in response to variations in receivedsignal strength, the control grid 69 of the amplifier or control device65 is connected to the output impedance through suitable controlelements comprising, in the present example, a potentiometer device |0|to which the control grid 69 is connected through a lead |93 and avariable tap connection |05. One end of the resistor IBI is connectedwith the cathode 61 and the opposite end is connected through a lead|01, a terminal |09, a variable series resistor and a supply lead ||3with the resistor preferably at the point of maximum negative potentialor terminal |5 as indicated.

Since the cathodes 61 and 1 are connected together, the biasingpotential developed across the output impedance is applied to the grid69 in response to signals, and the full amount of such potential isapplied to the grid 69 when the potentiometer IUI-|05 is adjusted to itsmaximum position with the contact |05 at the terminal to which the lead|91 is connected. A suitable bypass condenser ||5 is connected betweenthe lead 53 and the cathode 61 for filtering purposes in conjunctionwith the resistor which is also adjustable in value as indicated.

It will be seen that the output circuit of the high frequency rectifiernot only supplies signal and biasing potentials to the amplifierincluded therein, but also supplies a controlling or biasing potentialto the tone control device 65. Furthermore, automatic volume controlbiasing potentials at terminals indicated at ||1 are likewise derivedfrom the output impedance connection therewith including a lterimpedance H9.

Further control of the tone control network for variations in modulationpercentage is provided by a second rectifier device responsive to thevariations in the amplitude of the audio frequency signals delivered tothe circuit 35. In order that the audio frequency circuit may not beloaded thereby suliiciently to cause distortion of audio frequencysignals, the rectifier is coupled therewith by means of a bufferamplifier.

To provide this rectifier arrangement, an'electric discharge amplierdevice |2| is provided, and may be of substantially the sameconstruction as the device 5 including rectiiier and amplifier portions.The control grid |23 is connected to the audio frequency transmissioncirlead |35 having a tap connection |31 with the potential supply source8|.

Audio frequency signals in the circuit 35 are applied to the grid |23and are amplified in the device |2i, are applied to the anode |39 of thediode rectifier through a coupling condenser |4| and appear across therectifier output impedance or resistor indicated at |43. One end of theresistor is connected to the anode |39 and the o-pposite end isconnected to the cathode either directly or as shown, through a groundconnection |45, whereby a delay potential equal to the drop in the selfbias resistor |29 is provided for the anode |39.

It will be noted that one end |3, of the output impedance l of the highfrequency rectifier, and the positive end of the output impedance |43,of the audio frequency rectifier are connected to ground. Since thecathode 61 of the tone control device |2| is likewise so connected, thenegative potential from the negative terminal |5 of the impedance andthe negative potential at the terminal |41 of the output impedance |43may be applied to the control grid 69 in predetermined relation to eachother by the addition of a connection lead |43 from the terminal |131 tothe terminal |39 through a suitable series variable resistor indicatedat |5|.

With this circuit arrangement, it will be seen that the tone controlnetwork may jointly be controlled by the two rectiers. The plateimpedance of the control tube is normally reduced to a relatively lowvalue by means of a bias potential on the suppressor grid, while thecontrol grid is jointly controlled by potentials derived from rectierdevices in the signal circuit and the audio or modulation frequencycircuit, whereby the tone control means is placed jointly under controlof variations in both signal strength and percentage modulation.

When the rectified signal or high frequency and audio frequency currentsare Weak, providing a relatively low biasing potential on the controlgrid 69, the plate impedance is low and the tone control means causesthe predetermined portion of the audio frequency signal to beattenuated.

The control range of the tube 55 may effectively be increased by theaddition of external capacity coupling between the anode 63 and thesuppressor grid 13, as by means of a condenser |53 between them,together with a resistor |55 in circuit between the suppressor grid andthe bias impedance to be further lowered by increasing the change ofanode current resulting from a given change in anode potential.

Vxfhen compensated volume control means is provided in the audiofrequency transmission circuit, the source of rectified modulation oraudio frequency is taken preferably at a point preceding such volumecontrol means as at the point |51 in the present example, whereby theeffect of the automatic tone control may be independent of manual volumecontrol and may depend only on the strength of the high frequency signaland/or the percentage modulation. The automatic tone control meanscomprising the tube 65 is thereby actuated partly by rectified highfrequency currents and partly by rectified audio frequency currents.'Ihe ratio of control by the two differing currents is determinedprimarily by adjustment of the variable control elements and |5|.

In operation, during a lapse in modulation, for example, when a radioprogram is interrupted or is in process of change, the automatic tonecontrol means is effective to reduce the audio frequency band Width toprevent the transmission of noise signals through the audio frequencycircuit. When the modulation is resumed, the band width is automaticallyincreased again. Likewise, with a relatively weak high frequency signal,the audio frequency band width will also be reduced automatically, and,further, the compensated volume control device 4| may further modify thefidelity in a desired manner according to its construction andadjustment. The volume may also be adjusted by the contact 3|. However,the ratio of audio frequency to high frequency control of the tonecontrol means is changed thereby, as is obvious, because of the factthat the audio frequency control is derived from the audio frequencytransmission circuit following the device 5. Accordingly, the adjustmentat 3| preferably is xed and volume adjustments are then made at 49.

The effective control characteristic of the pentode device 65 is furtherillustrated by the curves shown in Fig. 2, to which attention is nowdirected.

In Fig. 2 the curves are plotted between plate current and plate voltagewith various negative biasing potentials on the control grid 69. Theanode impedance for the various curves, with a fixed plate potential,for example, of 250 volts, is indicated on each curve. tion experiencedwith certain types of tone control devices near the cut-off point of thecontrol tube is prevented by the pentode device, operated as hereindescribed and as shown in the drawing, and it will be seen from aconsideration of the curves that regardless of grid bias supplied by thehigh frequency and low frequency rectiers, the control tube of the typeshown may be operated at substantially zero anode current in the centerof the anode voltage anode current curve.

The combined high frequency and low frequency control voltages deliveredto the point |09 in the control circuit may both be controlled jointlyby operation of the potentiometer and together With the devices and |5|serve to completely adjust the relation of the two control voltages andthe amplitude of the combined control voltage resulting therefrom asapplied to the automatic tone control tube 65.

I claim as my invention:

1. In a radio signalling system, a detector, an audio frequency outputcircuit connected with said detector, a tone control network for saidoutput circuit including an electric discharge device as a controlelement therein, a rectifier connected with said audio frequency outputcircuit, electric discharge amplier means in said connection, means forderiving a controlling potential for said control device from saidrectifier, means for deriving a second controlling potential for saidcontrol device from the detector, variable means for jointly applyingsaid potentials to said control device, said first named electricdischarge device as a control element being of the pentode type having asuppresser grid and having a control grid for receiving said controllingpotentials, and means connected with said suppresser grid for applyingthereto a negative potential.

2. In a radio signalling system, the combination with a signaltransmission circuit, of a tone control network therefor comprising areactance device and a variable impedance means in series across saidcircuit, said variable impedance means The harmonic distorf' ingpotential comprising an electric discharge device havingacathodeconnected to one side of said circuit, an anode connected to theopposite side of the circuit through said reactance device, a controlgrid adjacent to the cathode, a suppressor grid adjacent to the anode,means for applying a [controlling potential to said control grid, meansfor deriving said potential jointly from a modulated high frequencysignal and from the modulation component thereof, means for applying anegative potential to the suppressor grid including a series resistor incircuit with said suppressor grid, an anode circuit impedance for saidanode in circuit therewith and a condenser providing coupling meansbetween said anode and the suppressor grid.

3. In a radio receiver, the combination with an audio frequency signalcircuit, of a tone control circuit, of a tone control network thereforincluding ari electric discharge device providing a control elementtherein and including a cathode, a control grid, a suppressor grid andan output anode, an impedance device and a reactance device in saidnetwork connected with said anode, a signal rectifier having an outputimpedance, an audio frequency signal rectifier having an outputimpedance, electric discharge amplifier means providing coupling meansbetween said last named rectifier and the audio frequency signalcircuit, means providing a variable connection .between each of saidoutput impedances and said control grid whereby variable biasingpotential is applied to said grid in response to variations in signalstrength and in the amplitude of the audio frequency signals in saidcircuit, and means for applying a negative potential to said suppressorgrid thereby to reduce the anode impedance of said device in the absenceof signals and audio frequency modulation.

4. A tone control system for radio receiving .apparatus and the like,comprising in combination a rectifier each for modulated and demodulatedsignals, a variable impedance tone control device responsive to avariable direct current biasfor controlling the impedance thereof, meansfor jointly applying controlling potentials to said tone control devicefrom said rectiers, and means for varying the relative values of saidcontrolling potentials.

5. A tone control system for radio receiving apparatus and the like asdeiined in claim 4, further characterized by the fact that one of saidrectiers is provided with a signal amplifier for applying thereto saidmodulated and demodulated signals.

6. In a radio receiving system, the combination with a signal detectorcomprising a diode rectiiier, of an audio frequency ampliiier forreceiving the rectied signal output from said detector having volumecontrol means, and tone control means including an electric dischargecontrol device, said control device comprising an anode, a cathode, acontrol grid adjacent to the cathode;l a vsuppressor grid adjacent tothe anode and a screen grid between said control and suppressor grids,means for applying rectied audio frequency signals to said control grid,means for applying rectified signals to said control grid from saiddetector, and means for operating said suppressor grid at a negativepotential thereby initially to reduce the anode impedance of saiddevice.

'7. A tone control system for radio receiving apparatus and the like asdefined in claim 4 further characterized by the fact said variableimpedance tone control device includes a pentode electric dischargeamplifier tube having a control grid for receiving said controllingpotentials and that means are provided for applying a negative p0-tential to the suppressor grid thereof, thereby to provide an initialpredetermined anode impedance.

8. In a tone control system, a diode triode electric discharge deviceconnected in circuit for detecting and amplifying a modulated Signal, asecond diode triode connected with the output of said iirst named devicefor amplifying and then rectifying an audio frequency signal, a pentodeelectric discharge control device for said system, means for derivingnegative controlling potentials from the rectiiied output of each ofsaid devices, means for independently applying said potentials to thecontrol grid of said pentode devices to vary the anode impedancethereof, and means for applying a negative biasing potential to thesuppressor grid of said pentode device to provide an initial relativelylow anode impedance.

9. In a radio receiving system, the combination with a signal detector,and an output circuit therefor, of a rectifier connected with saidoutput circuit, coupling tube means in said connection whereby saidrectifier is prevented from loading said output circuit, a tone controlnetwork for said system, a pentode tube in said network as a controllingimpedance element therein, and means for deriving controlling potentialsfor said pentode tube from said detector and rectifier to vary the anodeimpedance thereof, and means for reducing said anode impedance to aninitial low value.

10. A tone control system for radio receiving apparatus and the like,comprising receiving means for modulated signals, demodulating means forsaid signals, a rectifier each for said modulated and demodulatedsignals, said rectifiers each having an output circuit providingcontrolling potentials derived from said signals, a variable impedancetone control device in said receiving system responsive to controllingpotentials, and means for jointly applying controlling potentialsthereto from said rectiiiers, comprising a potentiometer resistorconductively connected with said output circuits and said tone controldevice.

VERNON D. LANDON.

CERTLFCATE OF CORRECTION Patent No. 2,09L\O75 September' 28, 195T VERNOND. LANDON.

It is hereby certified that error appears in the printed of the abovenumbered patent requiring correction as fol] ows: Page l., first column,line 55, for the word. ulength read strength; and that the said LettersPatent shouldbe read with this correction therein that the same mayconform to the record of the oase inthe Patent Office.

Signed and sealed this 16th da'y of November, A. D. 1957 Henry VanArsdale,

(Seal) Acting Commissioner of Patents.

specification

